Directory assistance services are provided to help telephone subscribers locate telephone directory numbers of other subscribers. The services are customarily provided by a directory assistance operator connected to the requesting caller via a switching system. Early designs of directory assistance systems required operators to refer to books and file cards to find the desired directory numbers. As directory assistance traffic increased, more efficient and automated techniques and systems were introduced to furnish the required service.
Conventional directory assistance services charge a fee to the caller for dialing the directory assistance service, and charge an additional fee if the caller elects to have the call completed by the directory assistance service. More recent directory assistance services are subsidized by advertising in the form of one or more recorded messages played to the caller.